Valve seal operation

[Patrick]

Hi fellas,
Dumb question... but how do the umbrella seals work? I just freshened up my stock 318 heads (lapped valves, new springs, keepers, locks, stock rubber seals) and while i was installing the seals it occured to me that they don't snap on - they just kinda lay there. Does the oil in the head keep the valve lubed enough so that it doesn't pull the seal up away from the head?
thanks!

 

[fishy68]

They act just like an umbrella, hence the name "umbrella seals". Just like an umbrella stops most of the water hitting you but not all they act the same. They don't stop all the oil but do a good job stopping 90-95% of it. The oil splashed on them mainly comes from the rocker arms which are above the valves so it just hits the umbrella and runs off back into the head. PC type seals that snap down over the guide (which has to be machined to accept them) stop 99% plus of the oil so their a little better.

 

[Patrick]

thanks Fishy.
But the seal manages to stay put even though nothing is holding it? Surprised that some may not get pulled up by the valve once in a while...?

 

[ramcharger]

They do get pulled up by the valve stem. No biggie, they work just fine as long as you don't have excessive valve guide clearance.

 

[C130 Chief]

Umbrella seals were typically designed into engines when guides were iron and some oil consumption (and therefore HC emissions) was tolerated. GM used an o-ring in the retainer and a metal splash guard on Chevy small blocks. Worked well, but used a bit of oil. Many British engines used no exhaust seal, and sometimes no intake as well. Flatheads never use a seal.

In the late 70's tighter seals were added to iron guide engines and guide life took a plunge. Most new engines have aluminum heads and bronze guides so they do fine with a tighter seal.

Personally I like umbrella seals, but run teflon PC seals with bronze guides.